The former US diplomat who chaired ill-fated talks on unresolved peace process issues in Northern Ireland has called on Stormont's parties to set out a clear timetable for striking an as-yet elusive deal.
Dr Richard Haass expressed disappointment that all five Executive parties have failed to reach consensus on a draft agreement produced at the end of six months of negotiations.
He insisted the essence of compromise meant no party could ever get everything it wanted.
The process chairman's latest statement came as leaders of Northern Ireland's four main churches united to encourage politicians to sustain momentum from the talks.
While Sinn Fein and the SDLP have endorsed Dr Haass's proposed blueprint for dealing with long running disputes on flags, parades and the legacy of the Troubles, the Democratic Unionists, Ulster Unionists and cross-community Alliance party have all demanded changes.
Alliance indicated its unwillingness to support the whole deal at the immediate close of the talks on New Year's Eve, while in recent days both the DUP and UUP have also confirmed they are not prepared to accept the proposals as they stand.
The UUP has effectively rejected the document outright, while the DUP has said much more work is needed to achieve consensus.
In a joint statement today, Dr Haass and talks vice-chair Dr Meghan O'Sullivan, a US foreign affairs expert, said: "We are pleased that some of the parties of the Executive have endorsed the agreement in its entirety and agreed to move forward on its implementation.
"We are disappointed that all five have not done so. Unquestionably, there are details that need further refinement, but these details should be honed in the necessary legislation and during implementation."
At the close of the talks, Dr Haass had recommended that a working group made up of the five parties be set up to take the process forward.
But even this proposal has been the source of disagreement.
While Sinn Fein believe the task of any such group should be solely to implement the agreement as it stands, the DUP want it to be used to hammer out amendments to the draft.
The US negotiators said: "We understand that no party is fully comfortable with every element of the text as finalised on December 31 2013.
"The draft reflects months of conversations with individuals and groups within Northern Ireland as well as the five parties. It reflects the often competing preferences of the five parties and what was required to bridge them.
"Our experience in Northern Ireland suggests that those who believe they can ensure that each and every element of the agreement is to their liking - and still secure five-party consensus - are being unrealistic in the extreme.
"Politics inevitably requires that each party accept some elements it views as disagreeable in order to advance the greater good; indeed, it is only through compromise that the political parties will be able to collectively deliver the better future that the people of Northern Ireland demand and deserve."
They added: "We call on the parties to make clear to the people of Northern Ireland their timetable for completion of an agreement and urge them to move speedily toward its implementation."
Earlier, senior Catholic, Church of Ireland, Presbyterian and Methodist clerics issued a joint statement applauding what they described as strenuous and sincere efforts to find solutions.
It stated: "As church leaders we encourage politicians to sustain the momentum and energy generated by the talks of the Panel of Parties in the Northern Ireland Executive, chaired and facilitated by Dr Richard Haass and his team.
"Significant work has been completed in recent months and we acknowledge the strenuous and sincere efforts put in by all involved in seeking to find solutions to some of the most contentious issues we face.
"This is an important time for our society; the momentum for building peace should not be lost."
The letter was signed by Catholic Cardinal Sean Brady, Church of Ireland Archbishop of Armagh Dr Richard Clarke, Presbyterian Moderator Dr Rob Craig, Methodist President Dr Heather Morris and Fr Godfrey O'Donnell, President of the Irish Council of Churches.
Members of the Protestant loyal orders today met with unionist politicians to discuss the situation.
Earlier this week, Sinn Fein Deputy First Minister Martin McGuinness accused "rejectionist elements" within the Orange Order of setting the agenda for the unionist parties.
In a joint statement, the Grand Orange Lodge of Ireland, the Royal Black Institution, the Apprentice Boys of Derry and Independent Loyal Orange Institution said: "While it is clear resolution regarding the three outstanding issues is proving difficult; that should not diminish the responsibility on all in society to find lasting solutions to these complex issues.
"For our part, the Loyal Orders remain committed to playing a positive role in the process going forward and pray for genuine cultural accommodation in keeping with a shared future."
Dr Haass was enlisted by Northern Ireland's ministerial Executive in July to broker a settlement on contentious issues which have sparked sectarian divisions.
Despite significant progress on dealing with tensions over more than 3,000 unresolved murders during past decades of conflict, the talks ended without any deal.
They followed months of sporadic loyalist violence over contentious parades, restrictions on the flying of the Union flag from Belfast City Hall and an increase in the number of bomb attacks by dissident republicans opposed to the peace process.
Disputes over contentious parades regularly erupt into street violence while differences over the flying of flags - on public buildings and in loyalist and republican neighbourhoods - cause community conflict.
Arguably the most complex issue has been how Northern Ireland deals with the legacy of a 30-year-conflict, with opposing sides retaining competing narratives of what happened and victims demanding truth and justice.
The proposed agreement does not envisage an imminent solution on flags, and instead proposed the setting up of the Commission on Identity, Culture and Tradition to examine the problem over a longer time-frame - potentially 18 months.
On parades, Dr Haass recommended the replacement of the oft-controversial UK Government-appointed Parades Commission with a new devolved mechanism for adjudicating on contentious events.
On the past, the document proposes a new Historical Investigations Unit to take on the investigatory responsibilities of the police's Historical Enquiries Team (HET) and the Police Ombudsman's office in regard to Troubles-related crimes.
For those victims searching the truth of what happened to their loved ones, even though justice has proved out of reach, the draft deal also proposes the creation of an Independent Commission for Information Retrieval (ICIR).
This would encourage those involved in killings to provide details with the assurance that their revelations could not be used against them in a court of law - a form of limited immunity from prosecution similar to that offered to those who decommissioned weapons during the Troubles and those who passed on information on the location of secretly buried victims of republican paramilitaries.